In the field of vending machines, it is well known to use a dispensing control means which calculates a preferred combination of coins for dispensing in the form of change. One typical way of achieving this, referred to as the "least number of coins" method, involves determining the total amount of change to be dispensed, calculating the maximum number of coins of the highest available denomination which in total have a value of equal to or less than the amount to be dispensed, deducting this amount to obtain a residual amount to be dispensed, taking the next lower denomination and determining the maximum number of coins which in total are equal to or less than this residual amount, deducting this total from the residual amount, and continuing using progressively smaller denominations until either the residual amount is equal to zero or the lowest denomination has been used. The object of this technique is to use as many higher-denomination coins as possible, so that the total number of dispensed coins is minimised. This maximises the number of coins retained in the stores so that change remains available for the maximum number of transactions.
It is important that the calculation of the combination of coins to be dispensed takes place quickly, so as not unduly to delay the user of the machine. In the past, this calculation has taken place at the same time as the dispensing. Thus, the highest value coins would be dispensed in turn, until the remaining amount to be dispensed became less than a single coin of this denomination. Then the next lower denomination would be dispensed in a similar manner. With such an approach, if insufficient coins of a low denomination are available, the user will be short-changed. In some machines, the user is given a warning of this possibility so that he can avoid using the machine, or so that he can select a vend price and/or the nature of the inserted coins in such a manner as to minimise the requirement for change. These warnings would be given in response to detecting a low level of availability of coins of the lowest denomination. For the warning to be reliable, the threshold level at which the warning was given was set to be considerably higher than would often be necessary, depending on the availability of higher-denomination coins. Accordingly, this warning was given unnecessary frequently.
In some known arrangements, the combination of coins to be dispensed is calculated before any coins are dispensed. This makes it possible with greater reliability to assess those situations in which insufficient coins are available to give the correct amount of change. However, these arrangements still suffer from a number of disadvantages. First, the method used to calculate the number of coins of various denominations did not always correctly give the combination which uses the least number of coins. This could happen even if coins of all the denominations handled by the machine were available. However, it would happen more frequently if certain of these coins were unavailable because the relevant stores had been depleted or because the mechanism for dispensing from those stores had malfunctioned. Second, the warning that sufficient change was unavailable would be given in circumstances when the correct amount of change could be provided by a different combination of coins.
U.S. Pat. No. 4,192,972 shows an arrangement which determines different combinations of coins (or other monetary units) deposited during the current transaction which can be dispensed as change, until there is determined a combination having a total value equal to the amount desired to be dispensed. However, this arrangement would often suffer from the first disadvantage mentioned in the preceding paragraph. Also, the technique used for determining the different combinations is unsuitable for minimizing the number of required calculations.
It would therefore be desirable to provide a technique for overcoming these problems.